Republicans have seized upon Vice President Joe Biden's unintentional
reference to slavery last week. It's a sign of how dirty this presidential
campaign has become, writes John Avlon.

"Look at what they value and look at their budget and what they're proposing. Romney...said in the first 100 days he's going to let the big banks once again write their own rules - 'Unchain Wall Street'. They're going to put y'all back in chains!"

So thundered Vice President Joe Biden about Mitt Romney in front of a largely African-American audience in Danville, Virginia. And with these words a new summer storm began.

Almost immediately, Team Romney responded with an angry statement: "After weeks of slanderous and baseless accusations against Governor Romney, the Obama campaign has reached a new low."

To European ears, the cause of such outrage might be hard to hear, but in the strategically quick-to-take-offence Romney campaign this was interpreted as an intentional invocation of slavery. That's right – there was Joe Biden pandering to a black audience by saying that Mitt Romney was going to enslave them if he was elected president.

No doubt the Veep's language was clumsy, but it was not intentionally race-baiting. Instead, here was a classic manufactured controversy, which successfully took over a day of the news cycle with less than 90 days until the election.

The closest metaphor is in soccer, when players feign injury in order to get a free kick awarded against the opposition. So too, now, in presidential campaigns.

It is part of an effort to claim the high-ground in a low campaign – play the victim and you just might earn some public sympathy. More importantly, you create the room to justify your own negative attacks in response.

The escalation is on – and as Martin Luther King once warned: "An eye for an eye leaves everybody blind."

And so Mitt Romney himself obligingly piled in that same night in Ohio, decrying – with genuine emotion – the state of the race as he saw it.

"Another outrageous charge came a few hours ago in Virginia. And the White House sinks a little bit lower. This is what an angry and desperate presidency looks like. Mr President, take your campaign of division and anger and hate back to Chicago."

Division and anger and hate: that's a serious charge. Politics can be a full contact sport, but objectively this has been a relentlessly negative campaign from both sides so far.

In fact, since the general election effectively began in April, 79 per cent of television ads have been negative according to one study – an all time high (or low). This has been boosted by millions of dollars in outside spending by Super-PACs, those unaccountable billionaire-funded entities whose sole purpose is to attack under the auspices of educating, while the political consultant class grows as rich as Croesus.

There are few bright moral lines in this murky world, but the invocation of slavery is one. Slavery is, of course, the original sin of the United States and its mark caused a psychic scar on our country that endures generations later.

When it comes to racial politics, both pro and con, this is far from uncharted territory for Team Obama. The Chicago campaign calmly countered with a handful of examples of prominent Republicans – including the newly minted vice presidential pick, Paul Ryan – speaking of "unshackling" businesses from the burden of excessive regulation.

That economic usage was at work in the vice-president's words as well, they argued. Moreover, Joe Biden is somewhat notorious for his propensity for putting foot in mouth.

But is there a double-standard?

After all, the would-be vice president in 2008, Sarah Palin, was roundly criticised for this tortured metaphor about the Civil War few months before: "It has taken all these years for many Americans to understand that the gravity, that mistake, took place before the Civil War and why the Civil War had to really start changing America. What Barack Obama seems to want to do is go back before those days, when we were in different classes based on income, based on colour of skin."

Or here are the words of former Republican presidential candidate Michele Bachmann, who infamously attacked the Obama health care reforms by saying: "This is slavery... It's nothing more than slavery."

Slavery metaphors are all odious but compared to Palin or Bachmann, the sometimes bumbling Biden was subtle and at least arguably unintentional.

Just for added context, Biden also said about Romney and Ryan in the same Virginia speech: "Ladies and gentlemen, as I said, they're both good men. But they have fundamentally flawed judgment, in my view."

This is a professional courtesy the Obama haters have never been quick to grant.

And then there's the obvious point: levelling charges of race-baiting at the re-election campaign of the first black president strains common-sense credibility, even if it resonates with a segment of the conservative populist base.

There has been too much hate in American politics of late as the political fringe blurs with the parties' base. It has further polarised discourse and made constructive compromise in Congress all but impossible.

This is the landscape the next president will inherit, no matter who wins in November. Hypocrisy and fear-mongering have taken the place of hope and change in this play-to-the-base campaign.

But a sense of perspective still can help separate the hype from the hate and throw a dose of cold water on an overheated body politic that tries to make even slavery into a partisan talking point.